It is well known that the efficiency of an antenna diminishes significantly as its dimensions decrease to much less than a wavelength. In such instances complex tuning networks are employed to match the antenna radiation resistance to the transmitter or receiver, where the major portion of the signal is dissipated in the matching network. For example, airborne towel-bar blades operating at VHF/UHF frequencies may exhibit gains as low as −30 dBiL in the lower segments of the operating band. Apostolos in U.S. Pat. No. 5,790,080, entitled “Meander Line Loaded Antenna”, discloses that an antenna design may be conceived on a volumetric basis rather than a planar basis, where the limitation on performance is governed by the well known Chu-Harrington relationship that allows an antenna aperture to be much less than a wavelength in its operating frequency band.
In vehicular or airborne applications where space is at a premium and there is a need for efficient antennas operating in the VHF/UHF bands, volumetric solutions to antenna problems are imperative. Additionally, modern systems employ polarization as a significant parameter during system processing and transmission. Consequently, not only must the antenna be compact, but it must also provide independent orthogonal linearly-polarized components to avail the system processors of polarization diversity.
A figure of merit for providing an efficient radiating element is the net gain expressed by the familiar relationship:G=ηD                where: G is the net gain of the antenna                    η is the antenna efficiency, and            D is the antenna directivityThe directivity of a radiator may be defined by the radiated beamwidth of the antenna:D=4π/θφ                        where: θ and φ are half-power beamwidths expressed in radians.        
With the directivity established by the beamwidths of the radiated element patterns, which cover a broad field-of-view and are reasonably stable with frequency, the improvement in antenna gain may only be achieved by maximizing the antenna efficiency η. In practice, this translates into optimizing the antenna input VSWR, the voltage standing wave ratio, over the operating bandwidth and employing elements with minimum insertion loss.
This present invention addresses the needs enumerated above, as well as other needs, such as radiating high pulsed and CW power during transmission.
The present invention is related to U.S. Pat. No. 6,853,351, entitled “Compact High-Power Reflective-Cavity Backed Spiral Antenna” by Mohuchy, and U.S. Pat. No. 7,372,424, entitled “High Power, Polarization-Diverse Cloverleaf Phased Array”, also by Mohuchy, issued on May 13, 2008, the contents of which are hereby incorporated by reference in their entireties.